This invention relates to a method of correcting transfer of a thin material such as printing paper in a thin material transfer apparatus which is applied to a photoprinting machine or the like, and also to a thin material transfer apparatus to which the correction method is applied.
Recently, a photoprinting machine which automatically prints a film image or the like on printing paper is widely used. Such a photoprinting machine has a thin material transfer apparatus comprising: a transfer roller which transfers printing paper; a sensor which detects the front end of the transferred thin material; and a cutter which is disposed downstream from the sensor. Roll-like printing paper which is drawn out from a magazine or the like is transferred to a cut position by the transfer roller, and then cut into a predetermined length. The cut printing paper is transferred to a print position, and then subjected to a printing process. The transfer roller is rotated by a DC motor or the like so as to transfer printing paper by a predetermined range in accordance with the number of transfer pulses supplied to the motor.
In such a photoprinting machine, the transfer range of printing paper is varied by a change of the diameter of the transfer roller which is caused by reasons such as wear of the roller or replacement of the roller. Even when the transfer roller is rotated by a specified transfer pulse number, therefore, an error occurs in the distance of the cut printing paper. When the sensor for detecting the front end of printing paper or the cutter for cutting printing paper is replaced with another one, the mounting position may be varied so as to change the mounting distance between the sensor and the cutter. The transfer range of printing paper is varied also by this change, with the result that, even when the transfer roller is rotated by a specified transfer pulse number, an error occurs in the distance of the cut printing paper.
When the transfer roller, the sensor, or the like is replaced with another one, therefore, an error in transfer of printing paper is corrected in the method described below.
First, printing paper is transferred by the transfer roller and the cutter continuously performs two cutting operations on the printing paper, thereby obtaining two cut sheets of printing paper (hereinafter, such a sheet is referred to as a cut sheet). The distance of the second cut sheet is measured and the difference between the measured distance and a reference distance is calculated. The number of transfer pulses required for transferring a predetermined length of the printing paper from the position of the cutter is changed on the basis of the difference to correct the transfer range from the cutter position. The above-mentioned measurement of the distance of the second cut sheet is performed because of the following reason. The first cut sheet has an error in transfer from the cutter position, and also an error in transfer from the sensor position to the cutter position. By contrast, the second cut sheet has only an error in transfer from the cutter position.
Next, the printing paper is rewound so that the front end is located in front of the sensor. Then, the printing paper is again transferred to the downstream side. After the front end of the printing paper reaches the sensor, the printing paper is transferred by a transfer pulse number which corresponds to the mounting distance between the sensor and the cutter and which has not yet been corrected. In succession, the printing paper is further transferred from the cutter position by a transfer pulse number which corresponds to the predetermined range and which has been corrected, and the printing paper is cut by the cutter, thereby obtaining a third cut sheet.
The distance of the third cut sheet is measured and the difference between the measured distance and the reference distance is calculated. The number of transfer pulses required for transferring the printing paper from the sensor position to the cutter position is changed on the basis of the difference to correct the transfer range from the sensor position to the cutter position. In this way, the correction of the transfer range from the sensor position to the cutter position is performed after the transfer range from the cutter position is corrected, because, when the sequence of the corrections is inverted, the measurement is affected by an error in transfer from the cutter position, and hence the correction cannot be satisfactorily performed.
In the above-described method of correcting a transfer error, two cut sheets are required for correcting the transfer range from the cutter position, and one further cut sheet is required for correcting the transfer range from the sensor position to the cutter position. Consequently, many sheets of printing paper are wasted for the correction of the transfer error. When the transfer range from the sensor position to the cutter position is to be corrected, the front end of printing paper must be returned to a position in front of the sensor, and therefore the working efficiency is lowered. When the corrections are performed in a wrong sequence, it is forever impossible to end the correction work.
The problems are produced not only in a process of cutting printing paper, but also in processes of cutting thin materials other than printing paper, i.e., cut sheets made of various kinds of material such as paper, a resin, and a metal. With respect to the contents of a process, furthermore, the problems are produced not only in a cutting process using a cutter, but also in processes performed by various kinds of processing units, for example, formation of perforations in a thin material by a perforating apparatus, or formation of an image by an image forming apparatus. In the case where a process is performed on a wide fixed region, such as that where an image is formed, the edge of the fixed region on the upstream side is called a processing unit.